44 The Patio and Cazo Process. 



soon as 3 to 4 flasks are ready, they are taken to the retorting 

 furnace, quemadero, Fig. 8, where they are set on end over holes 

 on the slab which forms the bottom of the furnace. This slab is 

 0.60 m. above the ground. The size of the furnace is very vari- 

 able, depending on the amount to be treated. It may have 

 places for 8 to 10 retorts. The amalgam is kept in place by 

 four narrow strips of iron set into the mouth of the flask, and 

 bent so as to cross it beneath the amalgam. The space be- 

 tween the upper and lower flasks is covered with an iron plate 

 full of holes 0.005 in. in diameter, which is luted to both the upper 

 and lower flask. There is no danger of the amalgam falling 

 out, except with an improperly managed fire. This furnace has 

 entirely superseded the old capellina. 



A wash of clay, about 0.005 m. thick, is put around the upper 

 flasks to protect them from the air. A brick wall laid up tempo- 

 rarily is then built round all the flasks, and a charcoal fire is made 

 inside of it. The first object of the fire is to dry the clay coating; it 

 is therefore made to burn very slowly at first, so as to make it dry 

 without cracking. When this h as been done a brisk fire is made over 

 the whole of the flasks. Water is kept constantly flowing into 

 the tank below the flasks, both to keep up the supply and to keep 

 it cool. The mercury driven out of the amalgam falls into the 

 water and collects there. 



The operation needs care. If the temperature is raised too 

 high, there is danger of melting the amalgam. If raised too 

 quickly, there is danger of explosion from the rapid forma- 

 tion of the vapors of quicksilver. If the heat is not high 

 enough, the bullion is impure from excess of mercury. As a pre- 

 caution against this, the purchaser has a right to heat the bars of 

 silver red hot to drive off any excess of mercury, but if the bars 

 melt while undergoing the process, the purchaser pays for them at 

 their weight before heating. If they do not, the weight after 

 heating is accepted. When the work is properly done, the silver 

 still contains one per cent, of mercury. The mercury collected 

 in the tank is not entirely free from silver, and must be strained. 

 The amalgam collected is called estrujon, is much drier than the 

 other amalgam, and is retorted by itself when enough has been 

 collected to make it worth while to do so. 



The retort silver, plata pasta, is refined in a small reverbera- 



